Barclays Bank may have to pay out up to £100 million to around 300,000 of its personal loan customers after making mistakes on their paperwork.
Up to 300,000 customers could be in line for a few hundred pounds from the issue, which dates back to October 2008.
It comes after the bank revealed it is facing a £50 million fine over claims it acted “recklessly” in its multi-billion-pound bailouts from Qatar in 2008.
A spokesman described the latest problem, which relates to arrears notices and statements, as “technical documentary errors”.
It was revealed in a 185-page bank document in which Barclays stated it has “identified certain issues with the information contained in historic statements and arrears notices relating to consumer loan accounts. It is therefore implementing a plan to return interest incorrectly charged to customers”.
A Barclays spokesman said: “Barclays has proactively reviewed information it has historically sent to its customers relating to interest charges where we have found technical documentary errors … Interest was not due on certain accounts during the period that Barclays made this mistake, and whilst no one has been mis-sold to, customers are entitled to have their interest payments returned.”
The spokesman added: “Any affected customer will be contacted by Barclays and customers do not need to take any action.”
Barclays is facing further complaint after the Financial Conduct Authority (FCA) accused it of agreeing £322 million of secret payments to Middle Eastern investors to secure their support for cash calls totalling more than £5 billion at the height of the financial crisis.
Barclays, which contests the FCA’s findings, said the fees relate to advisory services over five years.
It is also being probed by the Serious Fraud Office and regulators in the US, and admitted it does not know how much the final cost will be.